FIELD OF THE INVENTION
The invention relates to a method for detecting the dropping of one or more control elements into a reactor core. The invention also relates to a configuration for carrying out the method.
Nuclear reactors of power stations have so-called control elements which can be moved into and out of a reactor core in order to control the reactor.
A particularly critical malfunction situation occurs if one or more such control elements drop by mistake into the reactor core (in contrast to an intentional drop, for example for an emergency shutdown). The reactor can then no longer be controlled optimally. In a malfunction situation of that type, power densities and distributions that are unfavorable to the burnup of the fuel elements arise in the reactor core. In that case, the fuel elements are put at particular risk when peaks occur.
Malfunction situations of that type are very critical in terms of the operation of the reactor and of the safety of the power station. The dropping of control elements by mistake into a reactor core must therefore be detected quickly so that suitable counter measures can be initiated in good time.
In principle, the dropping of a control element in the reactor core can be detected by using effects on signals of reactor instrumentation. However, detection is not straightforward on account of the large number of control elements and the fact that the effects differ according to position.
A suitable number of vertically disposed detector groups are provided inside or outside the reactor core in order to determine the power and/or power density. As a rule, those detectors each output a signal which has an edge when one or more control elements pass them.
To date, the signals from one detector group (per control element or control element group) in practice have firstly been differentiated (in order to obtain a pulse) and then added, so as to provide a total signal pertaining to the dropping of a control element. However, it has been found that such a sum signal was not suitable for reliable fault detection in all cases, in particular due to signal noise.
In connection with controlling the power of a nuclear reactor, U.S. Pat. No. 4,548,784 discloses a method for detecting the dropping of at least one control element in a reactor core, in which signals from detectors disposed along the fall path of the control element are added and fed to a respective monitoring or evaluation device, with the addition being followed directly by averaging.